1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device of a form such that the displacement operation of a piezoelectric/electrostrictive element is transmitted to a pair of right and left movable parts to control a component to be controlled, which component is sandwiched and held by the other ends of the movable parts, or the displacement operation of a pair of right and left movable parts that sandwich and hold a component to be inspected on the other end is sensed by a piezoelectric/electrostrictive element to sense the characteristics of the component to be inspected.
2. Description of the Background Art
Referring to FIG. 1, a conventional piezoelectric/electrostrictive device having such a form is constructed in such a manner that a piezoelectric/electrostrictive element 10b is disposed on each of the outside surfaces of a pair of right and left movable parts 11, 12 constituting a base 10a. Movable parts 11, 12 are connected with each other by means of a connecting part 13 on one end thereof, and movable part bodies 11a, 12a extend towards the other end thereof. The other end of movable part bodies 11a, 12a are made into mounting parts 11b, 12b for mounting a component H such as a component to be controlled or a component to be inspected.
Mounting parts 11b, 12b protrude inwards by a predetermined width from the other end of movable part bodies 11a, 12a, so as to oppose each other by holding a predetermined interval. Component H is fixed to the inside surfaces (joining surfaces) 11b1, 12b1 of mounting parts 11b, 12b via adhesives h1, h2 on the side surfaces of component H, so as to be sandwiched and held by mounting parts 11b, 12b of movable parts 11, 12.
In a piezoelectric/electrostrictive device having such a form, if component H to be mounted is long in the longitudinal direction of the device, one must increase the length L4 of mounting parts 11b, 12b, as shown in FIG. 2. In this case, the total length L1 of the device is elongated by the amount of increase in the length L4 of mounting parts 11b, 12b. Thus, if the length h of component H to be mounted is equal to the length L4 of mounting parts 11b, 12b, the total length L1 of the device is restricted by the length h of component H.
On the other hand, in the case of mounting a long component H shown in FIG. 2 to mounting parts 11b, 12b, if the length L4 of mounting parts 11b, 12b are, for example, left as it is shown in FIG. 1 without being changed, the total length L1 of the device is unchanged irrespective of the length h of component H. However, in this case, the length L4 of mounting parts 11b, 12b will be shorter than the length h of component H, thereby decreasing the area of the joining surface (bonding area) on component H. Therefore, if an ordinary adhesive made of resin is used as adhesives h1, h2, the adhesive strength on component H decreases. Decreases in the adhesive strength on component H in the worst cases cause component H to be dismounted from mounting parts 11b, 12b. 
A component H having a large dimension h in the longitudinal direction will have a mass that is increased by the amount of elongation of the length h if the other dimensions and the density thereof remain unchanged. Therefore,if the bonding area is small, for example, if mounting parts 11b, 12b are each in a state shown in FIG. 1, the impact imposed upon each of the adhesives h1, h2 will be large, whereby component H is more liable to be dismounted from each of mounting parts 11b, 12b. 
In a piezoelectric/electrostrictive device having such a form, if component H is dismounted from one of mounting parts 11b, 12b, the other of mounting parts 11b, 12b must support component H to succeed receiving the impact applied to component H. In this state, component H is liable to be dismounted from the other mounting part, and also there is a fear that the supporting balance of the mounted state may be lost to cause the one supporting mounting part or the movable part connected thereto to be broken by the action of torsional force.
In order to meet this problem, one must use an adhesive having an extremely high adhesive strength; however, it is generally difficult to obtain a special adhesive that can ensure a sufficient adhesive strength no matter how small the bonding area is. Furthermore, there is naturally a limit even in the case of using an adhesive having such a special property.
In a piezoelectric/electrostrictive device having such a form, in the case of improving the device properties by increasing the displacement of mounting parts 11b, 12b, one must increase the amount of displacement of the movable part bodies 11a, 12a by increasing the length of the movable part bodies 11a, 12a of movable parts 11, 12. However, in order to increase the length of the movable part bodies 11a, 12a of movable parts 11, 12 without increasing the total length L1 of the device, one must reduce the length of mounting parts 11b, 12b. As a result of this, the bonding area of joining surfaces 11b1, 12b1 at the mounting parts 11b, 12b will be smaller to weaken the adhesive force of component H to joining surfaces 11b1, 12b1 of mounting parts 11b, 12b all the more, whereby component H will be more liable to be dismounted and drop off from joining surfaces 11b1, 12b1.
In a piezoelectric/electrostrictive device having such a form, in order to mount component H onto mounting parts 11b 12b of movable parts 11, 12, component H is bonded to joining surfaces 11b1, 12b1 generally through the intermediary of adhesives h1, h2 made of resin. However, adhesives h1, h2 made of resin will have a reduced hardness or reduced Young""s modulus when the temperature changes above room temperature. The temperature change of the state of use of piezoelectric/electrostrictive devices is, for example, of a degree within a range from room temperature to 100xc2x0 C. However, even in this temperature range, adhesives h1, h2 will be softened at a high temperature. For this reason, the distortion of adhesives h1, h2 when an external force is applied will differ greatly between the state of room temperature and the state of a higher temperature than this. Therefore, the device properties of the piezoelectric/electrostrictive device having this form will differ greatly at a state of high temperature, even though the device properties in a state of room temperature remain as originally set.
FIGS. 3 and 4 illustrate the operation state of the device at a low temperature such as room temperature and at a higher temperature than room temperature, respectively. The influence caused by such a temperature change (temperature variation) will be larger accordingly as the bonding area is smaller, because the distortion imposed upon the adhesive will be larger accordingly as the bonding area is smaller. Therefore, as the bonding area increases, the influence of the temperature variation will be smaller.
In a piezoelectric/electrostrictive device having such a form, if component H increases in size to increase its mass, fixing part 13 for fixing the device itself must support the combined mass of component H and the device itself. Therefore, if an impact is received, fixing part 13 is liable to be dismounted. If the length L2 of fixing part 13 is increased in order to increase the bonding area, the total length L1 of the device will also increase.
Thus, an object of the present invention is to increase the displacement of each movable part and to sufficiently ensure the bonding between each mounting part and the component as well as the fixation of the device itself without changing the total length of the device and without reducing the bonding area at the joining surfaces of the mounting parts in a piezoelectric/electrostrictive device having such a form. Further, an object of the present invention is to firmly mount the component and the device in the case where the component is especially large and heavy or in the case where a large adhesive strength is needed.
The present invention relates to a piezoelectric/electrostrictive device and a production method thereof, and is directed to a piezoelectric/electrostrictive device having a base including a pair of movable parts opposing each other and a fixing part that connects the movable parts with each other at one end thereof, wherein the piezoelectric/electrostrictive device has a piezoelectric/electrostrictive element disposed on at least one outside surface of the movable parts of the base.
Now, the piezoelectric/electrostrictive device according to the present invention is characterized in that the base includes a pair of long mounting parts disposed at the other end of the movable parts for mounting a component to be controlled or a component to be inspected, and the mounting parts extend for a predetermined length while holding slit-shaped gaps of a predetermined width along inside surfaces of the movable parts by being turned around at the other end of the movable parts.
In the piezoelectric/electrostrictive device according to the present invention, the fixing part constituting the base can be constructed to include a pair of slit-shaped gaps of a predetermined width disposed on the opposing sides of the fixing part and extending along the inside surfaces of the movable parts.
In the piezoelectric/electrostrictive device according to the present invention, the base is constructed with a ceramic laminate formed by laminating and calcining a plurality of ceramic green sheets in a large number, or constructed with a metal laminate formed by laminating and joining a plurality of metal plates in a large number, or constructed by bending one sheet of a flat plate made of metal.
In the piezoelectric/electrostrictive device according to the present invention, the slit-shaped gaps between the movable parts and the mounting parts constituting the base and/or the slit-shaped gaps along the movable parts of the fixing part can be set to have a dimension that does not restrict a displacement of the movable parts during an operation of the piezoelectric/electrostrictive device. Further, each mounting part and each movable part can be formed to have identical or approximately equal thicknesses. A component to be controlled or a component to be inspected is fixed onto inside surfaces of the movable parts constituting the base via an adhesive, and the piezoelectric/electrostrictive device can be used in a state in which the component to be controlled or the component to be inspected is sandwiched and held by the mounting parts.
A more specific construction of the piezoelectric/electrostrictive device according to the present invention is a piezoelectric/electrostrictive device having a base including a pair of plate-shaped movable parts opposing each other, a fixing part that connects the movable parts with each other at one end thereof, and mounting parts connected to the other end of the movable parts, the piezoelectric/electrostrictive device having a piezoelectric/electrostrictive element disposed on at least one outside surface of the movable parts constituting the base, characterized in that slit-shaped gaps intervene between the movable parts and the mounting parts, and a length L12 of the slit-shaped gaps is set to be larger than a length L5 of connecting parts that connect the movable parts to the mounting parts. In the piezoelectric/electrostrictive device, the length L12 of the slit-shaped gaps is at least two times, preferably at least five times, as large as the length L5 of the connecting parts.
Here, the length L5 of the connecting parts and the length L12 of the slit-shaped gaps in the piezoelectric/electrostrictive device refer to the dimensions of the sites as defined in the piezoelectric/electrostrictive device shown in FIG. 21.
A method of producing a piezoelectric/electrostrictive device according to the present invention is a method of producing a piezoelectric/electrostrictive device having a base including a pair of movable parts opposing each other, a fixing part that connects the movable parts with each other at one end thereof, and mounting parts that extend for a predetermined length while holding slit-shaped gaps of a predetermined width along inside surfaces of the movable parts by being turned around at the other end of the movable parts, wherein the piezoelectric/electrostrictive device has a piezoelectric/electrostrictive element disposed on at least one outside surface of the movable parts of the base.
Now, the first method of producing a piezoelectric/electrostrictive device according to the present invention is characterized in that a base block formed by laminating and calcining a large number of ceramic green sheets is adopted as a material for forming the base, and the base including the movable parts, the fixing part, and the mounting parts is formed by cutting the base block at a predetermined site along a lamination direction of the ceramic green sheets.
The second method of producing a piezoelectric/electrostrictive device according to the present invention is characterized in that a flexible and bendable flat plate made of metal is adopted as a material for forming the base, and the base including the movable parts, the fixing part, and the mounting parts is formed by stamping the flat plate into a shape that delineates a planar development of the base so as to obtain a stamped structure, and bending the stamped structure at a predetermined site.
The third method of producing a piezoelectric/electrostrictive device according to the present invention is characterized in that a base block formed by laminating and bonding a plurality of plates made of metal in a large number is adopted, and the base including the movable parts, the fixing part, and the mounting parts is formed by cutting the base block at a predetermined site along a lamination direction of the metal plates.
In the piezoelectric/electrostrictive device according to the present invention, each movable part constituting the base includes a long mounting part, whereby the joining surface of each mounting part is large and the area of bonding the component with each mounting part can be set to be large. For this reason, according to the piezoelectric/electrostrictive device, the adhesive force of the component to the joining surface of each mounting part is strong, so that the component will not be easily dismounted from each mounting part, thereby making it possible to construct a joining structure that is strong against impact. Further, it is possible to prevent a situation in which the separation of the component from one mounting part damages the other mounting part.
Also, in the joining structure, each mounting part extends for a predetermined length while holding a slit-shaped gap of a predetermined width along the inside surface of each movable part by being turned around at the other end of the movable part. For this reason, a joining structure having a strong adhesive force between each mounting part and the component can be constructed without increasing the total length of the device and without degrading the displacement characteristics of the movable parts.
Further, according to this joining structure, even if the component to be bonded to the mounting parts is large and has an increased mass to impose a large external force on the adhesive, a large bonding area can be ensured without increasing the total length of the device, so that the distortion per bonding area can be reduced. For this reason, according to the joining structure, the influence given to the device properties by the temperature change of the adhesive can be greatly restrained as compared with the case in which the bonding area is small, and the operation range in which the set device properties are exhibited in a stable state can be extended to a wide range from low temperature to high temperature.
In the piezoelectric/electrostrictive device according to the present invention, if slit-shaped grooves are provided on both sides of the fixing part constituting the base, the area of the fixing part can be increased, without increasing the total length of the device, by increasing the length of the grooves. By this, the bonding area that fixes the piezoelectric/electrostrictive device can be increased to provide a strong adhesive force, whereby the piezoelectric/electrostrictive device can be firmly fixed. Even if the component to be mounted onto the piezoelectric/electrostrictive device increases in size to have an increased mass and the fixing part must support the combined mass of the device and the component, the adhesive force can be sufficiently enhanced to stabilize the fixation of the device.
As a base constituting the piezoelectric/electrostrictive device according to the present invention, it is possible to adopt a base (first base) constructed with a ceramic laminate formed by laminating and calcining a large number of ceramic green sheets, a base (second base) constructed by bending one sheet of a flat plate made of metal, or a base (third base) constructed with a metal laminate formed by laminating and bonding a plurality of metal plates in a large number. In this case, the slit-shaped gaps between the movable parts and the mounting parts constituting the base are preferably set to have a slit width that does not restrict a displacement of the movable parts during an operation of the piezoelectric/electrostrictive device. Further, each mounting part and each movable part constituting the base are preferably formed to have identical or approximately equal thicknesses. By this, the influence given to the displacement characteristics of the movable parts by the long mounting parts can be restrained to the minimum.
The base can be produced as follows. The first base can be produced with ease by adopting a base block obtained by lamination and calcination of a large number of ceramic green sheets as a material for forming the base, and using means for cutting the base block at a predetermined site along a lamination direction of the ceramic layers to form the base. The second base can be produced with ease by adopting a flexible and bendable flat plate made of metal as a material for forming the base, and stamping the flat plate into a shape that delineates a planar development of the base so as to obtain a stamped structure, and bending the stamped structure at a predetermined site to form the base. The third base can be produced with ease by adopting a flexible and bendable flat plate made of metal and adopting a base block formed by laminating and bonding a large number of the flat plates as a material for forming the base, and using means for cutting the base block at a predetermined site along a lamination direction to form the base.
The piezoelectric/electrostrictive device according to the present invention can be used as active elements such as various transducers, various actuators, frequency region function components (filters), transformers, vibrators for communication or mechanical power, oscillators, and discriminators, as well as sensor elements for various sensors such as supersonic wave sensors, acceleration sensors, angular velocity sensors, impact sensors, and mass sensors. Particularly, the piezoelectric/electrostrictive device can be suitably used as various actuators that are put to use for displacement, positioning adjustment, and angle adjustment mechanism for various precision components of optical instruments and precision apparatus. Here, the piezoelectric/electrostrictive device according to the present invention is a concept used to encompass elements that convert electrical energy to mechanical energy and vice versa.